The invention relates to a nozzle arrangement for laser beam cutting, having a nozzle body surrounding a focused laser beam and with a passage opening for the laser beam, and having a nozzle sleeve which surrounds the nozzle body and forms with the nozzle body an annular gap which on the one hand has an inlet for a gas, and on the other hand has an annular opening assigned to the passage opening.
In order, for example, to be able to cut workpieces at a high operating speed by means of a laser beam, it is known to make use, for the purpose of blowing out the material from the cutting groove, of a cutting gas which is fed at high speed. The cutting gas speed is in the ultrasonic region in this case. DE 36 30 127 A1 discloses such a nozzle arrangement for laser beam cutting which has a frustoconical nozzle body which is adapted to the focused laser beam, surrounds the latter and has a passage opening for the laser beam, and which has a nozzle sleeve which surrounds the nozzle body concentrically and forms with the nozzle body a plurality of gas flow channels which are connected to a gas source and open on the workpiece side from the passage bore for the laser beam into a combining chamber which is formed jointly by the nozzle body and by the nozzle sleeve and from which a single gas jet flows out through an exit bore at supersonic speed given appropriate dimensioning of the pressure of the gas.
Furthermore, there is known from DE 44 02 000 A1 a nozzle arrangement of the above-named type in the case of which the exit cross section of the exit bore is virtually equal to the transitional cross section of the annular gap to the exit bore. In this case, the transitional cross section of the annular gap is to be dimensioned such that the gas is accelerated at most to the speed of sound.
EP 0 294 324 describes a laser processing tool in which the cooling of the nozzle leads an additional cooling gas outside the nozzle up to the nozzle tip. In this case, a concentric annular chamber is formed around the outside of the conventional nozzle, in which there is also arranged a sensor device which is likewise cooled. A disadvantage of this is that supplying cooling gas at very high operating speeds leads to strong eddies at the nozzle exit, resulting in a rapid decrease in the speed of the gas. Moreover, such eddies lead to impairment of the result of cutting and, in particular, to impairment of the surfaces.
It is the object of the present invention to create a nozzle arrangement of the above-named type in which both the assembly of the nozzle arrangement and its fitting on a laser head is facilitated, and the guidance of the protective gas flow is improved.
The achievement of this object is promoted by providing a nozzle-like constriction in the annular gap.
This nozzle-like constriction has the advantage of achieving inside the annular gap a Venturi effect which leads to a substantial increase in the rate of flow. If appropriate, in this case the rate of flow can be greater than the speed of sound. This ensures that cutting slag still adhering in the cutting gap is blown away, thereby substantially improving the quality of the cutting gap.
There is also simultaneously a quicker cooling of the cutting gap, and this likewise leads to an improvement in the surface. In addition, it is ensured that oxygen is prevented from access to the cutting gap, so that oxidation is prevented when cutting metal.
A further substantial advantage resides in the fact that the use of gas is reduced although there is at the same time an increase in the speed of the gas. The pressure at which the gas is fed can thereby likewise be reduced.
As a rule, it would appear to be advisable for the constriction to be of annular configuration. This can be achieved chiefly either by crowning the outer surface of the nozzle body, or else by having a rampart-like elevation project from an inner surface of the nozzle sleeve.
The constriction should be configured such that a width of the annular gap is increased upstream and downstream of the constriction. This means that the gas expands slightly downstream of the constriction.
The assembly of the nozzle arrangement is facilitated, on the one hand, by providing spacers in the annular gap between the nozzle body and nozzle sleeve. These are preferably in this case longitudinally running ribs which are mounted on the outer surface of the nozzle body and/or the inner surface of the nozzle sleeve, or are formed from these surfaces.
Also serving the ease of assembly is a union nut by means of which the nozzle arrangement can be fixed on a laser head, for example a support sleeve. An inner flange of the union nut in this case strikes an annular shoulder of the nozzle sleeve, while the union nut as a whole is screwed on an external thread of the support sleeve.